Electric arc smelting furnaces are used to re-manufacture steels from scrap metals. The scrap metals are heated to a high temperature sufficient to melt the metals to a liquid form. The molten steel then can be processed for further uses.
The melting process imposes much thermal, chemical and mechanical stresses on the furnaces. Consequently, much attention and effort must be given to the structural integrity of the furnaces to assure safe operation and production. Frequent maintenance schedules must be maintained on the furnaces, thereby making recycling of steel very costly. In an attempt to alleviate the stresses, and to lower the operating cost of recycling steels, liquid cooling systems are installed on the furnaces. One such cooling system is disclosed in U.S. Pat. No. 4,207,060, which utilizes a series of cooling pipe coils. Generally, the coils are formed from adjacent pipe sections with a curved end cap welded to the ends of adjacent pipes to form a serpentine path for a liquid coolant flowing through the coils. The coolant is forced through the pipes under pressure to maximize heat transfer.
End caps on the cooling coils typically have two different shapes, curved or rectangular. While rectangular end caps are easier to manufacture, when liquid coolant passes through a rectangular end cap, the corners of the end cap tend to cause turbulent flow, bubbles, and vapor, which reduce thermal conductivity and cause localized overheating. Therefore, greater strength is required for rectangular end caps.
Curved or semi-circular end caps allow for a smoother, more laminate fluid flow. Thus, heat transfer efficiency is increased by maximizing surface contact between the coolant and internal coil surfaces. Also, localized overheating is reduced and strength requirements are decreased.
The junction where the two pipes join the end caps is an important area of concern for efficient and safe operation of an electric arc smelting furnace. At this junction, liquid coolants experience a sharp 180 degree turn and a change in fluid pressure. The change in fluid pressure at the junction can be caused by a slower speed of flow, a drop in flow volume, a greater friction between the liquid and the surface of the end caps, a formation of air bubbles, a formation of vapors, a dead flow area, a collection of mineral deposits due to the irregular shape of the welding compounds, a turbulent flow, and a greater heat accumulation due to a slower rate of thermal conductivity.
Also, since forced fluid flow generates high pipe pressure, the end cap and the parallel pipes must be welded strong enough to withstand the pressure. The only welding surfaces of known end caps are the rims, which makes welding difficult between the cap and the pipe ends, particularly in the valley area between the adjacent pipes.
Therefore, a primary objective of the present invention is the provision of an improved cooling pipe system for electric arc furnaces.
Another objective of the present invention is the provision of improved end caps for coiled cooling pipes of an electric arc furnace.
Still another objective of the present invention is the provision of cooling pipe end caps which improve the structural integrity of the liquid cooling system in electric arc furnaces.
A further objective of this invention is the provision of an end cap for the cooling system of an electric arc furnace which reduces turbulent fluid flow, reduces or eliminates the formation of bubbles and vapors in the coolant, and enhances the thermal conductivity of the furnace liquid cooling system.